There are two ways to approach this: If x is a linear function of the parameter, t, i.e. x= at+ b, when t= 0, x= 2, when t= 1, x= 4, what are a and b? If y is a linear function of the parametre, t, i.e. y= ct+ d, when t= 0, y= -1, when t= 1, y= 2, what are c and d? If z is a linear function of the parameter, t, i.e. z= et+ f, when t= 0, z= 3, when t= 1, z= -1, what are e and f?